Its capital is Yamagata city.
During the Heian Period (794–1185), the Fujiwara (藤原) family ruled the area. Yamagata City flourished during the Edo Period (1603–1867) due to its status as a castle town and post station, famous for beni (red safflower dye used in the production of handspun silk). In 1689, the famous haiku poet, Matsuo Bashō visited Yamagata during his five-month trip to the northern regions of Japan.- more in the wikipedia -

Legend about the Kappa living in river Mogamigawa 最上川に住む河童Once upon a time
there lived a village headman at the banks of river Mogamigawa - and he had a very beautiful daughter!
She was his only daughter and he loved her so very much and cared for her lovingly.
But one day all of a sudden her face became all pale green and she got worse every day.
He called a doctor to cure her, but he did not know the reason for her illness. And the girl herself also did not know what had gotten into her all of a sudden.

So the desparate father went to the miko 巫女 Shinto shrine shaman lady to have a look at the girl. The miko knew the answer:
"This is the deed of a Kappa. Seems a Kappa has taken a fancy to your daughter. If you can get hold of a skilfull Buddhist priest, he can perform a ritual of "Cutting off the Road" (michi kiri 道切) to catch the Kappa."

So the village headman went to an old temple and asked the priest to perform the exorcism rites 道切りの呪文.
The priest went to the river Mogamigawa, from where the Kappa made his entry into the village, and began his prayers and chanting.
As he was praying, the waters receeded very fast.

"Let go of the spell you put onto the headman's daughter, old Kappa!
Bring us a written statement 証文 that you will never harm anyone in this village and leave it here until tomorrow morning. If you do not comply, I will take away all the water of this river!"

When the priest called out his request, there was a feeble answer from the river:
"Ok, Ok, please wait until tomorrow morning!"

From the next morning on, the daughter was free of the evil spell and beautiful as ever.
And at the front gate of the temple where the priest lived there was a scroll with the promise of the Kappa.

It seems this scroll is still held in honor at a temple in Takahata.
Just to think that there was a priest who could retract all the water of the river Mogamigawa!

At the part where the main road enters a village, Dososhin deities are enshrined, sacred 注連縄 shimenawa ropes (or sometimes snakes made of straw) and other amulets are hung and 草履 zori (or waraji) straw sandals are offered to the deities in order to prevent evil spirits and monsters (or Kappa in this story) from entering and drive them away.

A straw figure at the roadside to ward off evil influence: . O-Ningyoo Sama お人形様 O-Ningyo Sama .
Figures of "boundary deities" sakaigami 境神 like this were put at the entrance of a village to ward off evil.